As is well known, a wide variety of locks are available for use on doors. However, most of these use a cylinder type bolt look operated by a key. Combination locks are in limited use in applications that do not require a finished appearance, such as on a warehouse door, for instance. Of the hidden type locks, the key type account for the maJor proportion regardless of the application, both in home and commercial use.
In key operated locks, however, the lock can be opened only with its key or a master key. So the lock cannot be operated when the key is lost. Statistics reveal that locking errors occur extremely frequently because the operation of the key is forgotten, and key locks are not preferred from the aspect of crime prevention.
It is of course possible to fit a dial lock as is used in a safe to a door, but the use of a dial lock in an ordinary door is impracticable due to structural limitations as well as design conditions.
To cope with these problems, a so-called button lock has recently been proposed, which can be fitted to the door surface and operates a dead bolt in accordance with a combination by a button operation However, the memory mechanism used in this lock has an extremely complicated construction and is expensive to produce. If the combination is fixedly set during production of the lock, users of the lock cannot change the button combination so as to meet their various requirements, and since a common combination cannot be set, those who sell and fit the locks cannot easily handle and properly set them for operation.